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Cannabis-associated respiratory disease can refer to neoplastic processes or to structural damage to the lung.

It is often compared to the damage done by tobacco, but it is the subject of much less study. Cannabis is sometimes considered more dangerous because filters are usually not used, and sometimes considered less dangerous because different molecules are involved.

The process most popularly used to ingest cannabis is smoking, and for this reason most research has evaluated health effects from this method of ingestion. Other methods of ingestion may have lower or higher health risks. Tobacco smoking has well-established risks such as bronchitis, coughing, overproduction of mucus, wheezing, and addiction. Similar risks for smoking cannabis related to airway inflammation have been suggested in a 1998 study of 40 healthy cannabis users who exhibited similar early characteristics to tobacco smoking.

The effects of tobacco and cannabis smoking differ, however, as they affect different parts of the respiratory tract: whereas tobacco tends to penetrate to the smaller, peripheral passageways of the lungs, cannabis tends to concentrate on the larger, central passageways. One consequence of this is that cannabis, unlike tobacco, has not been shown to cause emphysema, though this claim is disputed by Martin Johnson, MD, of the department of respiratory medicine at Glasgow (Scotland) Royal Infirmary . A 2002 report by the British Lung Foundation estimated that three to four cannabis cigarettes a day were associated with the same amount of damage to the lungs as 20 or more tobacco cigarettes a day. Unlike tobacco, regular cannabis use does not appear to cause chronic obstructive pulmonary disease.

In some cases, cannabis users mix commercial tobacco in joints, called "Spliff" (popular in Europe), tobacco mixed with hash in a chillum (India), or cannabis rolled in tobacco leaves (a blunt), which would expose the user to the additional risks of tobacco, such as rapid physical addiction to nicotine.

UCLA study

On 23 May 2006, Donald Tashkin, M.D., Professor of Medicine at the David Geffen School of Medicine at UCLA in Los Angeles announced that the use of cannabis does not appear to increase the risk of developing lung cancer, or increase the risk of head and neck cancers, such as cancer of the tongue, mouth, throat, or esophagus. The study involved 2252 participants, with some of the most chronic marijuana smokers having smoked over 22,000 marijuana cigarettes. The finding of Donald Tashkin, M.D., and his team of researchers in 2006 refined their earlier studies published in a Dec. 17th 2000 edition of the peer-reviewed journal Cancer Epidemiology Biomarker and Prevention. Many opponents of marijuana incorrectly cite the original finding of UCLA Medical Center from 2000 as "proof" that marijuana leaves the users at higher risk for cancer of the lung, and cancerous tumors, even though the researchers at the UCLA Medical Center have revised their finding with a more in-depth study on the effects of the use of marijuana. This seemed to contradict assumptions made after some studies, like those from Dale Gieringer et al., which found that 118 carcinogens were produced when marijuana underwent combustion, and two carcinogens {2-Methyl-2, 4(2H-1-benzopyran-5-ol) & 5-azulene-3,8-dione} formed when marijuana underwent vaporization with the Volcano Vaporizer. To help explain this seemingly chemical proof of carcinogenicity inherent in the process of combustion, Tashkin noted that "one possible explanation for the new findings, he said, is that THC, a chemical in marijuana smoke, may encourage aging cells to die earlier and therefore be less likely to undergo cancerous transformation."

In a study of ten smokers with mild respiratory issues Hii et al. found evidence of lung disease in the form of severe bullae (fluid-filled, thin-walled blisters) of different shapes and sizes. Despite such lung disease, the patients' chest x-rays were normal and lung function was only mildly reduced in nearly half of the patients. The cannabis-smoking patient group was, on average, 41 years old—considerably younger than previously research tobacco-smoking patients with lung disease, who had an average age of between 62–67 years. The researchers conclude that the younger age of lung disease and poorer lung function may be due to different smoking patterns demonstrated in cannabis smokers, who have been found to inhale larger amounts of smoke, which is held in the lungs for longer periods of time.

References

1. http://www.ncbi.nlm.nih.gov/pubmed/9517614
2. http://www.webmd.com/lung/copd/news/20000320/regular-marijuana-emphysema
4. Tashkin DP, Simmons MS, Sherrill DL, Coulson AH (1997). "Heavy habitual marijuana smoking does not cause an accelerated decline in FEV1 with age". American Journal of Respiratory and Critical Care Medicine. 155 (1): 141–8. doi:10.1136/thx.2006.077081. PMID 9001303. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
5. Australian Government Department of Health: National Cannabis Strategy Consultation Paper, page 4. "Cannabis has been described as a 'Trojan Horse' for nicotine addiction, given the usual method of mixing cannabis with tobacco when preparing marijuana for administration."
6. ^ "Study Finds No Link Between Marijuana Use And Lung Cancer". Science Daily. 2006-05-26. Retrieved 10-12-2011. {{cite news}}: Check date values in: |accessdate= (help)
7. Fred Gardner (2006-07-06). "Marijuana Smoking Does Not Cause Lung Cancer". {{cite news}}: Unknown parameter |org= ignored (help)
8. Tashkin, D. P., Simmons, M. S., Sherrill, D. L., and Coulson, A. H. 1997. Heavy habitual marijuana smoking does not cause an accelerated decline in FEV1 with age. American Journal of Respiratory and Critical Care Medicine 155(1): 141-148. Retrieved on 5 March 2007
9. Cite error: The named reference UCLA study was invoked but never defined (see the help page).
10. Researchers At UCLA's Jonsson Cancer Center Report Smoking Marijuana May Increase Risk Of Head And Neck Cancers, Sciencedaily.com, 1999-12-20, retrieved 2011-04-20
11. Cite error: The named reference TumorGrowth was invoked but never defined (see the help page).
12. Sarafian TA, Kouyoumjian S, Tashkin D, Roth MD (2002). "Synergistic cytotoxicity of Delta(9)-tetrahydrocannabinol and butylated hydroxyanisole". Toxicol. Lett. 133 (2–3): 171–9. doi:10.1016/S0378-4274(02)00134-0. PMID 12119125. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
13. Gieringer D., St. Laurent J., and Goodrich S. (2008). "Cannabis Vaporizer Combines Efficient Delivery of THC with Effective Suppression of Pyrolytic Compounds". Journal of Cannabis Therapeutics. 4 (1): 7–27. doi:10.1300/J175v04n01_02. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
14. Hii, S.W., Tam, J.D.C., Thompson, B.R. & Naughton, M.T. (2008). Bullous lung disease due to marijuana. Respirology 13, 122-127
15. "NCPIC Cannabis and tobacco factsheet". Ncpic.org.au. 2011-03-11. Retrieved 2011-04-20.

• Articles to be merged from May 2013
• Cannabis smoking